1. Field of the Invention
The present invention relates to a linear guide apparatus including a guide rail, and a slider supported through balls on the guide rail and movable in the axial direction, and in particular, to an improvement in a dust proof structure of the guide rail.
2. Description of the Prior Art
In a prior art linear guide apparatus, a slider is mounted on an axially extending guide rail through many rollable balls so that the slider is movable linearly. The guide rail is secured to a base by tightening securing bolts which are inserted through a plurality of bolt holes formed by penetrating a trunk portion of the guide rail. The slider, having a driven member attached thereon, moves along the guide rail. Furthermore, since the dust, dirt, chips, etc., deposited on the upper surface of the guide rail disturb smooth rolling of the balls, wiper seals for removing dust deposits are fixed to opposite ends of the slider.
In such a structure, when the securing bolts are tightened to secure the guide rail to the base, the bolt heads sink in the bolt holes, and recesses are formed in the upper surface of the guide rail. Thus, dust and the like deposited in the recesses will intrude into the inside of the slider passing under the wiper seals to disturb the smooth movement of the slider. For this reason, it has been generally practiced to apply embedding plugs into the recesses. However, it is very difficult to completely eliminate the stepped portions formed between the plug heads and the upper surface of the guide rail surrounding the bolt holes, and dust is still deposited in any remaining recesses. Moreover, another problem is involved in that lip portions of the wiper seals are caught by the edges of the recesses resulting in changes in the sliding resistance of the wiper seals.
Accordingly, the inventors of the present application previously proposed a linear guide apparatus which has no stepped portions at the bolt holes (Japanese Utility Model Laid-Open Publication No. 59-116401).
In the proposed linear guide apparatus, as shown in FIGS. 1 and 2, a linear channel 1a is formed in the upper surface of a guide rail 1 to extend in the longitudinal direction. A head 4A of a bolt 4 for securing the guide rail 1 to a base 3 is accommodated in the linear channel 1a, and a male thread portion 4B of the bolt 4 is threaded into a threaded hole 6 of the base 3 through a bolt hole 5 formed penetrating the guide rail 1. furthermore, a dust proof plate 7 extending in the longitudinal direction, of guide rail 1, is mounted on the opening of the linear channel 1a. The dust proof plate 7 is made of synthetic resin, and has a flat trapezoidal cross section. The opposite side surfaces of the dust proof plate 7 are formed with engaging ridge portions 8, and corresponding recess portions 9 are formed in the linear channel 1a. After the guide rail 1 is secured to the base 3 by bolt 4, the dust proof plate 7 is inserted into the linear channel 1a from one end of the guide rail 1 to cover the opening of linear channel 1a.
However, in such a prior art linear guide apparatus, the dust proof plate 7 is fixed to the guide rail 1 only by fitting ridge portions 8 and recess portions 9 to each other, and no securing means for clamping is provided. As a result, when the sliding resistance of the wiper seals is large, the dust proof plate 7 on the guide rail 1 slides and moves in the axial direction, thereafter the linear channel 1a and the bolt head 4A are exposed allowing dust to be deposited thereon. Moreover, the problem of high manufacturing cost has been involved since it is necessary to form the ridges on the dust proof plate 7 by using a metal mold, and since it is also necessary to form the recess portions in the guide rail 1.